1. Field of the Invention
The present invention relates to silver halide photographic emulsions and especially to silver halide photographic emulsions in which the sensitivity of the fine grain silver halide crystals in the emulsion to electron beams is increased remarkably by adding a specific compound to the emulsions.
2. Description of the Prior Art
In the preparation of silver halide photographic emulsions, chemical sensitization methods, namely, sulfur sensitization by thiourea derivatives or sodium thiosulfate, reduction sensitization by stannous chloride or hydrazine, and gold sensitization by salts of noble metals such as gold, platinum and palladium are well-known processes for increasing sensitivity. However, sensitization of photographic materials to be used for electron beam recording is insufficient by these known methods.
The electron beam recording process is capable of high density recording. In order to obtain an image having high quality by this process it is necessary that the silver halide particles of the sensitive material be as small as possible. However, because reducing the particle size of the silver halide particles generally brings a lowering of electron beam sensitivity, it is necessary to develop a new sensitization process. It is also important to reduce the surface charge of the sensitive element at exposure to the electron beam in order to obtain a distinct image. Accordingly, it is necessary, to reduce exposure, to increase the speed of the electron beam-sensitive element and consequently a sensitive element having a high electron beam sensitivity is required.
In short, in preparing sensitive elements used for electron beam recording, it is required to prepare silver halide photographic emulsions containing silver halide crystals the particle size of which is as small as possible and having a high electron beam sensitivity. This is an important problem in the art of sensitization to electrons.